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Introduction to Antarctica, Why is it so Cold?

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Introduction to Antarctica and
the Antarctic,
Why is it so cold?
Jean Pennycook
Antarctica or Antarctic?
Antarctica is the 5th
largest continent on
earth and larger
than the US and
Mexico combined.
The word,
“Antarctica”, refers
to the continent
itself. “Antarctic”
refers to the entire
southern polar
region, including
the ocean that
surrounds this
Most of Antarctica is covered with over 2 km of snow and ice.
These large glaciers move toward the coast under their enormous
weight and the force of gravity. When a portion floats out over the
ocean these extensions are called ice shelves. The Ross Ice Shelf
is as large as Texas.
Source of diagram
unknown.but thank you!
Ross Ice Shelf
This is the edge of a glacier that is floating on the
water, but is connected to the remainder that is on the
Picture courtesy of:
The ice shelf from the ocean. What you see is only 10% of
the height of this mass of ice. 90% is under the water. This is
fresh water and was made from snow fall.
The amount of ice in Antarctica plays a very influential role in the Earth’s
temperature. Ice reflects most of the sunlight back into the atmosphere
without absorbing it. This helps keep the Earth cool.
This map shows
the continent of
Antarctica. The
glaciers are white
and the ice
shelves are in
gray. Red dots
indicate a
science research
Map courtesy of Australian Antarctic Data Centre
So much for Antarctica but what about the Antarctic? It
is best defined by ocean boundaries, although
politicians usually define it by latitude for convenience.
Here is one definition:
Any place whose latitude is
greater than 66.5o S. In this
case here is a map of the
Antarctic, defined by what is
called the Antarctic Circle. It
would include most of the
continent of Antarctica and
be defined as all places that
receive at least one 24 hours
of daylight period and one 24
hours of darkness once a
year. This boundary would
never change as it is defined
by latitude.
Another definition, and
the one used by
scientists, would be
everything south of the
Antarctic Polar Front.
The polar front or,
Antarctic Convergence,
is where the cold
Southern Ocean, which
encircles Antarctica,
meets the warmer
northern water. This is
what the Antarctic
defined in that way would
look like. This boundary
changes slightly
seasonally and over the
You have two definitions of what
“Antarctic” means and what area of the
Earth would be included. Are there any
other ways to define this region? How
would you draw the map?
Why are the Polar regions colder
than the rest of the Earth?
Imagine a flat Earth
Consider the black line the total amount of
sunlight energy received by the Earth
Now imagine the earth is tilted.
Is the amount of sun energy hitting the
Earth more or less?
Would the Earth be colder, warmer or the
Is the amount of energy more or less?
Would the Earth be colder, warmer or the
Hint: Is the black line bigger or smaller?
Let’s tilt it some more
Now what is happening?
Even more. . . . . .
You get the idea. . . .
What would the earth be like in this
Each of these sun’s
rays are equal in size
and therefore amount
of energy, but notice
at 45o angle the
amount of land
covered by the ray is
larger than when the
angle is at 90o.
Translate what you just learned to the energy coming
from the sun to our Earth’s surface. Where is the angle
of the sun 90o and where is the angle very low or no
sun at all?
Source of diagram unknown
In this diagram you see the angle of the sun is marked for the various
places on the Earth. The Earth is in this position with respect to the sun on
the equinoxes.
Source of diagram unknown
The Earth is tilted with respect to the sun and this is how the angles of the
sun translate as the Earth rotates around it. These angles change with the
season. Notice that the sun is at a 90o angle at latitude 23.5oN. This is the
Tropic of Cancer and no place north of this line will ever see the sun at 90o.
Source of diagram unknown
Position of the Earth on
the Equinoxes
Position of the Earth on
the Solstices
The angles of the sun’s rays rotate from the extremes of these two
diagrams. Notice at the North and South Poles the angle of the sun never
gets greater that 23.5o above the horizon. The latitudes where the sun’s
angle is 0 at mid-winter are called the Arctic and Antarctic Circle,
respectively (66.5 N & S). The low angle of the sun in the polar
regions is one reason why these places are so cold.
Source of diagram unknown
As the angle of the sun gets smaller towards the poles the amount of
energy received by the earth is not a linear relationship. It is a function
of the angle as you see in the chart below
SIN 80 = 0.98 or 98%
SIN 70 = 0.94 or 94%
SIN 60 = 0.87 or 87%
SIN 50 = 0.77 or 77%
SIN 40 = 0.64 or 64%
SIN 30 = 0.50 or 50%
SIN 20 = 0.34 or 34%
SIN 10 = 0.17 or 17%
SIN 0 = 0.00 or 0%
Translate: If the angle of the sun is 80o then that region receives
98% of the energy it would if the sun were 90o. Or places on the
Earth where the sun is 60o above the horizon receive 87% of the
energy that a place where the sun is straight up or 90o receives.
Insolation is the amount of sun energy hitting the earth
at a given place.
The total amount of energy hitting each of these latitudes in a year is
represented by the number of boxes under the curve. Notice the
amount hitting the poles is much smaller than the rest of the earth. This
is another reason why the poles are so cold.
Source of diagram unknown
Day / Night Cycle Graph
Before you go the next slide predict how this graph will change if you go north,
say to Iceland where the latitude is 64.1o N, very near the Arctic Circle.
Did you guess right? Because Reykjavik is near the Arctic Circle there are
periods of almost 24 hours sunlight and periods of almost darkness all
night. Now let’s go to a place above the Circle say Thule, Greenland.
Before you go to the next slide predict what the graph will look like.
Did you predict correctly? Since Thule is above the Arctic Circle there are
days of 24 hours sunlight and nights of 24 hours of dark. How would this
graph change if we went to a similar latitude in the South? Predict first
then go the next slide.
How did you do? Believe it or not this is almost the exact same graph as the
one for Thule only the seasons are reversed because McMurdo is in the
Southern Hemisphere. Two more: Predict what this graph looks like at the
Equator and at the South Pole.
At the South Pole the sun goes below the horizon on the spring solstice
(March 21/22) and does not reappear until the fall solstice (Sept 21/22)
The same happens at the North Pole only reversed.
Six months of darkness is another reason the Polar regions are so
You have seen how the orientation of the earth has made for
unequal heating of the Earth’s surface. Because of the angle
of the sunlight at the Poles they receive less energy and are
therefore much colder than the rest of the Earth. You have also
seen that the daytime-nighttime cycle provides long periods of
darkness for the polar regions which also promote a colder
Are the poles equally cold?
Compare the average T at the North and South Poles
Average Winter oF
Average Summer oF
South Pole
North Pole
Notice that the South Pole average summer temperature is colder than the
average winter temperature at the North Pole
Come up with some ideas why this is so.
The Arctic is a large body of water surrounded by land, but the Antarctic is a
large land mass surrounded by water. This is one reason the Antarctic is
colder than the Artic.
These maps show the ocean currents for both polar regions. Compare the
patterns of the currents. The cold Antarctic water moves in a circular path
around the continent and since there are no land masses to deflect it north there
is little mixing with those warmer waters. This is quite different from the
Arctic and is another reason the Antarctic is colder than the Arctic
Remember this slide? Another reason that the Antarctic is colder
than the Arctic, is that the average altitude of Antarctica is almost
2 kilometers. All other things being equal, the Earth’s atmosphere
decreases by 6.5oC for every 1000 m of altitude that you ascend (
or about 3.5oF per 1000 ft).
Source of diagram
unknown.but thank you!
The cold air descends and spreads across the surrounding sea…
Cold air descending
from the higher altitudes
and blowing over the
continent towards the
coast is another reason
why Antarctica is colder
than the Arctic.
From Parrish & Cassano 2001, J Climatology
In winter, the outward
spreading cold winds
help to freeze the
ocean surface, and
the “ice area” of
Antarctica (land plus
sea ice) doubles. In
spring all this ice
reflects sunlight,
keeping the ocean
colder for longer.
Sea ice in
During the summer,
without the coldest
winds and the
Incessant sun, the
sea ice melts around
most of the continent,
but only for a month
before the ocean
starts to freeze again
as the sun dips lower
and lower.
Sea ice in
To sum things up:
• Antarctica is a continent almost completely covered with ice and snow
and is influential in keeping our planet cool by reflecting the sun’s energy
back into space.
• The Antarctic is a region and has more than one definition.
• Both Polar regions are colder than the rest of the Earth due to the
reduced angle of the sun providing less energy, and long periods of
darkness when no sun energy arrives.
• Antarctica is a colder place than the Arctic because it is a land mass and
surrounded by a very cold ocean that does not mix with warmer waters in
the north.
• Antarctica is also colder because it is so high in altitude.
Other Powerpoint presentations for you classroom:
Introduction to the Polar regions, Why is Antarctica so cold?
Introduction to Adelie Penguins, Adelie Penguins march into the classroom.
Penguin Adaptations, This is a harsh continent
Adelie Penguin Behavior, Good manners are always in style
Penguin Predation and Competition, Life is tough for an Adelie Penguin
Adelie Penguins Cope with Global Climate Change
Did You Know, How researchers know what they know
Penguin Quandaries, Can you answer these mysteries
Fun pictures about Adelie Penguin
Go to The education page.
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